Gas-supported rolling diaphragm seal for piston and cylinder assembly

ABSTRACT

A piston and cylinder element in an assembly as in a compressor or hot gas engine, with a rolling diaphragm seal secured between these elements, with supporting gas on both sides of the seal and a constant pressure differential maintained across the seal.

llited taies Patet 1 1 Meijer et al.

[ Jan. W74

GAS-SUPPORTED ROLLING DIAVHRAGMI SEAL FOR PISTON AND CYLINDER ASSEMBLYInventors: lRoelf .lan Meijer; lilendrilk Alphons .laspers, both ofEmmasingel, Eindhoven, Netherlands Assignee: ILLS. Philips Corporation,New

York, NY.

Filed: Dec. 23, 1371 Appl. No.: 21 1,406

Related US. Application Data Continuation of Ser. No. 26,580, April 8,1970, abandoned.

U.S. c1 92/83, 60/24, 92/98 1) 1m. c1. FlSb 21/1141, Fl6j 1/19 Fieldram- 92/60, 83, 98 11 [56] References Cited UNITED STATES PATENTS1,085,818 2/1914 Oxnard 92/98 x Primary ExaminerMartin P. SchwadronAssistant Examiner-Abe Hershkovitz Attorney-Frank R. Trifari [5 7ABSTRACT A piston and cylinder element in an assembly as in a compressoror hot gas engine, with a rolling diaphragm seal secured between theseelements, with supporting gas on both sides of the seal and a constantpressure differential maintained across the seal.

12 Claims, 5 Drawing Figures PAIENTEDJH m4 3783.745 sum 10; s

Fig.1

INVENTORS ROELF' J.MEIJER HENDRIK AJASPERS BY ix-Li i AGEN PATENIEDJAN81974 3.783.745 SHEET 20F 5 INVENTORS ROELF J.ME|JER HENDRI K AJASPERSAGENTU PATENTEB JA 8 I974 SHEEI 30? 5 IN VENTORS HENDRI K A.JASPERSROELF J-MEIJER PATENTEDJAK 8 I974 SiEH HJF 5 Fig.3

INVENTORS AGENT PATENTEDJAN 8|974 3.783745 SIEEI S0? 5 INVENTORS AGENTGAS-SUPPORTED ROLLING DIAPHRAGM SEAL FOR PISTON AND CYLINDER ASSEMBLYThis is a continuation, application Ser. No. 026,580, filed Apr. 8,1970, now abandoned.

BACKGROUND OF THE INVENTION The invention relates to a device comprisingat least one cylinder in which a piston is adapted to reciprocate, withone end of the piston defining and varying the volume of a working spacecontaining a working medium, the other end of the piston bounding aremote buffer space containing a compressible medium; at least onerolling diaphragm is provided between the piston wall and the cylinderwall for separating a first space from a second space, while asubstantially constant pressure difference prevails across the rollingdiaphragm. Devices of this kind are known and may be utilized withhot-gas reciprocating engines, cold-gas refrigerators, compressors, andthe like.

In a device known from French Patent No. 1,326,063, the first spaceforms part of the working space and the second space is filled with asupporting liquid. The rolling diaphragm is provided for preventing gasfrom leaking out of the working space and impurities such as lubricantsfrom penetrating into said space.

To the second space (the liquid space) can be supplied liquid(lubricant) by pump means; a controlmember ensures that a quantity ofliquid is conducted out of the liquid space such that, with a rollingdiaphragm having its concave side facing the gas space, the pressuredifference across the diaphragm does not drop beneath a given minimumvalue; and with a rolling diaphragm having its convex side facing thegas space,

' this pressure difference does not exceed a maximum No. 1,326,063.The'device in accordance with the in-v vention is characterized in thatbetween those parts of the piston and cylinder walls which are locatedbetween the rolling diaphragm and the working space, at least one firstseal is provided which separates the first space from the working space,the second space also containing a compressible medium at a pressurewhich exhibits constantly an approximately constant difference from thepressure prevailing in the first space. Owing to the first seal betweenthe first space, and the working space the pressure variations occurringin operation in the working space are not admitted into the first space.The pressure variation in the first space is therefore independent ofthat in the working space. The second space now also contains acompressible medium (gas) whose average pressure, when the concave sideof the diaphragm faces the first space, is lower than the averagepressure in the first space. Conversely, if the convex side of thediaphragm faces the first space, the average pressure in the secondspace exceeds that of the first space. Y The pressure in the first spacehas always a difference from the pressure in the second space. Becauseit is ensured that no pressure variations can occur either in the firstspace or in the second space, or because the phases and amplitudes ofthe pressure variations occurring in said spaces are equal to eachother, the pressure in the first space will always differ by thesameamount from the pressure in the second space. In this way a device isobtained in which the rolling diaphragm is supported by a gas instead ofbeing held by a liquid, while it is ensured that the gas pressure on oneside of the diaphragm differs by a constant value from the gas pressureon the other side of the rolling diaphragm. The dein said space, whichare at least approximately equal to and in co-phase with the pressurevariations occurring in the further space and the second spacecommunicating therewith, while the average pressure in the first spacediffers from that in the further space and in the second space.

The term effective diameter of the rolling diaphragm'has to beunderstood to denote the diameter of the seal which would have the sameeffect as the rolling diaphragm and which lies approximately midway between the diameters of the surfaces along-which the diaphragm is adaptedto roll.

The end of the piston facing the remote space, upon movement of thepiston in the cylinder, will vary the volume of the remote space andhence the pressure in the remote space and in the second spacecommunicating with the former, to an extent suchas will be determined,for example, by the active surface of said end and by the stroke of thepiston. By an appropriate choice of the volume of the first space and ofthe diameter across which the seal is operative, it is ensured that witha given differing pressure level in the first space and in the secondspace the pressure variations occurring in the latter space areapproximately equal to and in phase with the pressure variationsoccurring in the first space.

I An advantageous embodiment of the invention is a hot-gas reciprocatingengine of the displacer type, in

. which the displacer connecting rod is passed through the piston; apartfrom the rolling diaphragm between the piston wall and the cylinderwall, which separates the first space from the second space, at leastone additional or second rolling diaphragm is provided between thepiston and the displacer connecting rod, which separates a third space;from a fourth space, the parts of the piston and the displacerconnecting rod located between the second rolling diaphragm and theworking space have arranged between them at least one second seal whichseparates the third space from the working space, the third spacecommunicating with the first space and the fourth space communicatingwith the remote space, while the first seal and the second seal are eachoperative across a diameter which differs from the effective diameter ofthe rolling diaphragm or of the second rolling diaphragm respectively,so that the resultant volume variations upon a movement of the pis' tonand the displacer produce pressurevariations in the first, and thirdspaces at least approximately equal to and in phase with the pressurevariations in the remote space and in the second and fourth spacescommunieating with the former, while the average pressure in the firstand third spaces differs from that in the second and fourth spaces.

The pressure variations occurring in the remote space and in the secondand fourth spaces communicating herewith as a result of the movements ofthe piston and of the displacer connecting rod, which are moving with agiven relative phase difference, are consequently compensated for bypressure variations produced in the first and third spaces at a pressurelevel in the second and fourth spaces which differs from the pressurelevel in the first and third spaces. Therefore with suitably chosenvolumes of the first and third spaces and their communicating channel(5), and with a suitably chosen diameter on which the seals between thefirst and third spaces and the working space are operative, asubstantially constant pressure difference will always prevail on therolling diaphragms.

A further advantageous device embodying the invention is characterizedin that between the parts of the piston wall and the cylinder walllocated between the rolling diaphragm and the remote space at least oneadditional third seal is provided, which separates the second space fromthe remote space, the first and third seals being operative across thesame effective diameter as the rolling diaphragm.

The pressure variations occurring in the remote space upon a movement ofthe piston will no longer become manifest in the second space due to theprovision of the third seal. Since both the first seal and the thirdseal are both operative on a diameter which is equal to the effectivediameter of the rolling diaphragm, the volumes of the first and thirdspaces, upon a movement of the piston in the cylinder, will remainsubstantially constant. Consequently, these spaces will exhibitsubstantially no pressure variations so that, because the pressure levelin the first space differs from that in the second space, asubstantially constant pressure difference will always prevail on therolling diaphragm.

A further advantageous device embodying the invention, is formed by ahot-gas reciprocating engine of the displacer type, in which thedisplacer connecting rod is passed across the piston; and apart from therolling diaphragm between the piston and cylinder walls separating thefirst space, from the second space at least one additional rollingdiaphragm is provided between the piston and the displacer connectingrod, which separates a third space from a fourth space. This embodimentis characterized in that between the parts of the piston and thedisplacer connecting rod located between the additional rollingdiaphragm and the working space, at least one second seal is providedwhich slepa rates the third space from the working space, while betweenthe parts of the piston and the displacer connecting rod located betweenthe additional rolling diaphragm and the remote space at least onefourth seal is provided which separates the fourth space from the remotespace; the first and third seals are operative on ations in the remotespace resulting from relative movements of the piston and the displacerconnecting rod and the cylinder passed to the second and fourth spacesrespectively owing to the presence of the third and fourth sealsrespectively. Since furthermore the first and second seals are operativeon a diameter which is equal to the effective diameter of the rollingdiaphragm, while the third and fourth seals are operative on a diameterwhich is equal to the effective diameter of the further rollingdiaphragm, the volumes of the first, second, third and fourth spacesremain constant upon relative movements of the piston, the displacer rodand the cylinder.

Therefore, no pressure variations occur in said spaces, so that therolling diaphragm and the additional rolling diaphragm always have aconstant pressure difference at the constant, but differing pressurelevels in the first and second spaces and the third and fourth spacesrespectively.

In a further advantageous device embodying the invention, the firstspace is in open communication with the third space and the second spacewith the fourth space. This provides the advantage that if slightpressure variations should occur in one of the spaces, for example dueto inaccuracies of dimensions of the structural parts (tolerances),these pressure variations are levelled out in the larger overall volumeof the space in which the slight variations occur and in the spacecommunicating therewith.

A further advantageous device embodying the invention is characterizedin that the remote space is formed by a hermetically closed crank casingaccommodating a driving gear connected with the piston (or the pistonand the displacer respectively) and a generator or an electric motorcoupled therewith. The device formed by a hot-gas engine having agenerator coupled with the driving gear of the crank casing, theelectric conductors connected to the generator being taken through thewall of the crank casing to the outside, is extremely suitable foroperating for a long, uninterrupted period as an independently operatingsource of electric energy, while owing to the very simplifiedconstruction of the device inspection is carcely required or even notnecessary. If the crank casing of the device formed by a cold-gasrefrigerator comprises an electric motor, the unit thus obtained can bereadily transported and leaves any freedom in the arrangement of, forexample, measuring apparatus in laboratories in lowtemperature researchwork.

- In a further advantageous device embodying the invention, the sealsare'formed by piston rings accommodated each in a groove in the wall ofthe piston of the cylinder or displacer connecting rod respectively,there being constantlyan open communication between the space in theassociated groove behind the piston ring and one of the two spaceslocated on either side of the piston ring and being adjacent thereto. Ifthe open communication is constantly present between the space in thegroove behind the piston ring and the working space or the spacerespectively'an average pressure will be established in operation of thedevice in the space between the rolling diaphragm and the piston ring,because the piston ring seal allows a free stream of gas towards theworking space and the further space respectively, which average pressurewill be lower than the average pressure prevailing in the working spaceand in the space respectively and approaching the minimum pressureprevailing in said space.

However, if the open communication is established between the space inthe groove behind the piston rod and the space between the rollingdiaphragm and the piston ring, the average pressure established in thelatter space, because the piston ring seal allows gas to pass in theother direction, will exceed the average pressure occurring in theworking space and the space respectively and be approximately equal tothe maximum pressure in said space.

An adjustment of an average pressure in the first space exceeding theaverage pressure in the working space may be desired in the case inwhich the rolling diaphragm is provided as a seal between the piston andthe cylinder of a compressor having a suction pressure lower thanatmospheric pressure. An adjustment of an average pressure in the firstspace lower than the average pressure in the working space isadvantageous when the second space is in open communication with theremote space so that with a given pressure difference across the rollingdiaphragm a lower pressure level will suffice in the second space and inthe remote space.

. The open communication may be established by providing the piston ringwith radial grooves on a side facing either of the two spaces separatedby the piston ring or by providing a bore in the piston, the cylinder orthe displacer connecting rod respectively.

In a further advantageous device embodying the invention the seals areformed by narrow gaps. The pressure variations in the working space andthe remote space are not transferred by these gaps to the spaces betweenthe rolling diaphragms and the gaps. However, gas leakage occurs so thatin the operation of the device an average pressure is established in thespaces adjacent the rolling diaphragm, which pressure will be at leastapproximately equal to the average pressure in the working space and theremote space respectively.

A further advantageous device embodying the invention is characterizedin that the compressible medium in the second, fourth and remote spacesis the same medium as that in the working space. In a furtheradvantageous device embodying the invention a channel is provided whichjoins at one end the working space and at the other end the remotespace, said channel including a by-pass valve, which may bespring-loaded and which opens towards the space faced by the concaveside(s) of the rolling diaphragr'n(s).

In practice a slight diffusion of medium across the rolling diaphragmwill always occur from one side of the diaphragm of the higher pressure,the concave'side, towards the other side of the lower pressure, theconvex side. Therefore when the rolling diaphragm has its concave sidefacing the working space, medium will leak away from the working spaceto the remote space or conversely; when the rolling diaphragm has itsconvex side facing the working space, medium will diffuse from theremote space into the working space. In the course of time the pressurelevels in the working space and in the remote space will level out,which may result inthat the pressure .-diffe'rence across the rollingdiaphragm becomes too low and the rolling diaphragm may be damaged byfolds. I

By an appropriate choice of the initial pressures in the working spaceand in the remote space and in the spaces adjacent the upper and-lowersides of the rolling diaphragms it is now simply possible by means ofthe channel with the by-pass valve to return medium diffused from thehigher-pressure space across the rolling diaphragm into thelower-pressure space to the firstmentioned space.

In this case the pressure variations occurring in the working space andin the remote space respectively are utilized. After the diffusion ofmedium from the higherpressure space into the lower-pressure space thepressure occurring in the lower-pressure space for a fraction of asecond may exceed the pressure simultaneously prevailing in thehigher-pressure space. It is therefore possible for medium to passduring this fraction of the period via the by-pass valve from thelowerpressure space to the higher-pressure space so that the initialpressure difference across the rolling diaphragm is re-established.

The invention will be described more fully with reference, by way ofexample to the drawing which shows a few embodiments of devicescomprising rolling diaphragms seals schematically not to scale.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a devicecomprising a rolling diaphragm seal supported by a gas, the space insidethe rolling diaphragm being separated by a piston ring seal from theworking space.

FIG. 1a shows the pressure variation in the various spaces of thisdevice.

FIG. 2 is a sectional view of a hot-gas engine of the displacer typecomprising rolling diaphragm seals with gas support, the spaces insidethe two rolling diaphragms being separated by piston ring seals from theworking space.

FIG. 3 is a sectional view of a device comprising a rolling diaphragmseal with gas support, the space above and the space below the rollingdiaphragm being separated by a piston ring seal from the working spaceand the further space respectively.

FIG. 4 is a sectional view of a hot-gas engine of the displacer typecomprising gas-supported rolling dia phragm seals the spaces inside thetwo rolling diaphragms being separated by piston ring seals from theworking space, while the space beneath the rolling diaphragms isseparated by piston ring seals from the crank casing.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring toFIG. 1, referencenumeral 1 designates a cylinder iniwhich a piston 2 is adapted to move,the upper side of which is capable of varying the volume of a workingspace 3, which contains working medium. The piston 2 is connectedthrough a piston rod 4 with a driving gear (not shown) and has anannular surface 9 on the bottom side. Between the cylinder 11 and thepiston 2 a rolling diaphragm 5 provides the seal and separates amedium-containing space 6 from a space 7 containing a compressiblemedium (gas) at an average pressure lower than the average pressure inthe space 6 so that the rolling diaphragm 5 has its concave side facingthe space 6. Between the piston wall and the cyl-. inder wall a pistonring 8 is accommodated in a groove of the piston wall, separating theworking space 3 from the space 6.

There is furthermore provided a return duct 3'1, which communicates atone end with the working space 3 and at the other end with the space 7.This duct includes a spring-loaded bypass valve 32, which opens in thedirection towards the working space 3. The piston ring 8 is provided onthe lower side with radial grooves. Thus there is always an opencommunication between the space in the groove behind the piston ring andthe space 6, so that in the operation of the device leakage of workingmedium will occur mainly from the working space 3 to the space 6.Therefore an average pressure will be established in the space 6, whichpressure will be approximately equal to the maximum pressure prevailingin the working space 3. This may be advantageous, for example, incompressors, when medium of atmospheric pressure is sucked into theworking space.

If it is desired in this case to use a rolling diaphragm having itsconcave side facing the working space, it is necessary for keeping therolling diaphragm in taut state, to maintain a pressure difference of afew atmospheres, for example, 5 atms., in the direction to the space 7.If in contrast to the construction of FIG. 1, the space 6 is in opencommunication with the working space, the rolling diaphragm is subjectedat a given instant to a pressure in the working space which is lowerthan the desired space difference across the rolling diaphragm. When thepressure in the working space drops further, the rolling diaphragm willno longer be stretched to the desired extent. This difficulty is nowcompletely obviated by the adjustment of the maximum pressure in thespace 6 and in the working space 3 in the manner described above.

The establishment of the maximum pressure may be accounted for asfollows: When the pressure in the working space 3 exceeds that in thespace 6, the piston ring 8 is urged by its lower side against the lowerface of the groove. However, working medium can then always leak fromthe working space 3 along the radial grooves on the lower side of thepiston ring 8 to the space 6. If the pressure in the working spacedecreases to below the pressure in the space 6, the piston ring comesinto contact by its top side with the top face of the groove and willseal the working space 3 with the exception of a slight leak. As aresult the average pressure in the space 6 will exceed the averagepressure in the working space 3 and be approximately equal to themaximum pressure in said space.

The open communication between the space in the groove behind the pistonring 8 and the space 6 may be obtained in a different way, for example,by providing a bore in the piston. The piston ring 8 has an effectivediameter D, exceeding the effective diameter of the rolling diaphragm 5.If the piston 2 moves over a distance y in downward direction, therolling diaphragm will be lowered in an average over a distance of %y.The space 7 will then exhibit a reduction of volume substantially equalto y X S, wherein S is the surface of the annular face 9 of the piston2. Since the diameter of operation of the piston ring seal .8 is largerthan the effective diameter of the rolling diaphragm, the space 6 alsoexhibits a reduction of volume when the piston 2 moves downwards overthe distance y. The reduction of volume amounts to:

1 2 a y wherein D is the outer diameter of the gap accommodating therolling diaphragm and D is the inner diameter. When the piston 2 movesdownwards, the pressure in the space 7 and in the space 6 increases dueto the reduction of volume. Conversely, an upward movement of the piston2 brings about an increase in volume and a decrease in pressure in thespaces 6 and 7.

The pressure level in the space 6 is higher than that in the space 7. Bya suitable choice of the nominal volume of the space 6 and of thediameter of operation of the piston ring 8, the pressure variationsproduced by the movement of the piston in the cylinder in the space 6are equal to and in phase with the pressure variations occurring in thespace 7. Consequently, an at least substantially constant pressuredifference will prevail across the rolling diaphragm in each stroke.

In practice a slight amount of medium will always diffuse from the space6 of the higher average pressure through the rolling diaphragm into thespace 7 of the lower average pressure. Medium disappearing from thespace 6 is replenished from the working space 3 as described above.After some time such a quantity of medium may have diffused through therolling diaphragm from the working space 3 and the space 6 to the space7 that the pressure difference across the rolling diaphragm becomesinadmissibly small so that the diaphragm may become defective by theformation of folds. By means of the return duct 31 including the bypassvalve 32 medium can be returned from the space 7 to the working space 3,when the nominal pressure levels in these two spaces are suitablychosen. This will be explained further with reference to FIG. la.Therein p designates the pressure variation in the working space 3 forone period; the curves for p, indicate two different pressureadjustments in the space 7.

The pressure in the space 7 is in phase opposition to the pressure inthe working space 3. The pressure level in the space 7 is lower than inthe working space. The

maximum pressure prevailing in said space is equal to the minimumpressure in the working space 3, which pressures appear at the sameinstant in operation of the device. The pressure variation p in thespace 6 is equal in phase and amplitude to that in the space 7, whilethe pressure level is approximately equal to the maximum pressure in theworking space 3 owing to the effect described to the piston ring 8.

When medium diffuses from the working space 3 and the space 6 throughthe rolling diaphragm S to the space 7, so that the pressure level inthe working space 3 decreases and that in the space 7 increases, thecurves p and p will intersect each other near the point A. p,, is thenmomentarily higher than p, so that medium can be fed back through thebypass valve 32 from the space 7 into the working space 3. The bypassvalve 32 is arranged so that it allows medium to pass only in thedirection from the space 7 to the working space 3.

In FIG. 1a the solid curve of p, applies to the situation in which thebypass valve 32 is not loaded by a spring, so that the pressure'in thespace 7 can never exceed that in the working space 3. The pressuredifference across the rolling diaphragm is then of the magnitude of thedifference between the maximum and minimum pressures in the workingspace 3, which difference may be fairly high in given circumstances. Ifa lower pressure difference across the rolling diaphragm is desired, thebypass valve may be loaded by a spring, as is shown in FIG. 1, so thatit opens not until the pressure difference exceeds a given minimum valvecorresponding to the counter-pressure exerted by the spring. Then thepressure variation in the space 7 of the kind indicated by a broken linein FIG. 1a is obtained.

In this way a device is obtained in which a constant pressure differenceprevails always across the rolling diaphragm in operation wihout theneed for the liquid support of the diaphragm, pumping means andcontrolmember conventionally used in the known devices. Altough inaccordance with the invention the noncompressible liquid support isreplaced by a support of the rolling diaphragm by a compressible medium,the aforesaid measures ensure nevertheless that the rolling diaphragm isnot affected by variations in length so that its lifetime is long.

FIG. 2 is a sectional view of a hot-gas engine; corresponding parts aredesignated by the same reference numerals as in FIG. 1. In a cylinder 1a piston 2 and a displacer 110 are adapted to reciprocate. The piston 2varies by its upper face the volume of a compression space 11, whereasthe upper face of the displacer varies the volume of an expansion space12. These two spaces communicate with each other via a cooler 13, aregenerator l4 and a heater and are filled with working medium. Thepiston 2 is fastened by a hollow piston rod 4 to a yoke 16, whereas thedisplacer 10 is connected with a yoke 18 by a displacer rod 17, passedthrough the piston 2 and the hollow piston rod 4. The yokes 16 and 18form part of a rhombio driving gear designated by 19 and arranged in thespace 7, forming a crank casing and also containing working medium.

Between the cylinder 1 and the piston 2, a rolling diaphragm 5 separatesa space 6 from the space 7. There is furthermore provided a rollingdiaphragm 20 between the piston 2 and the displacer rod 17, saiddiaphragm separating a space 21 from the space 7. The space 6communicates through a channel 22 freely with the space 21. Therollingdiaphragms ensure that working medium of the compression spacecannot penetrate into the crank casing and impurities such aslubricating oil cannot pass from the crank casing 7 into the compressionspace 11.

Between the piston wall and the cylinder wall and the piston wall andthe displacer rod wall piston rings 8 and 23 respectively are provided,which are each accommodated in a groove in the piston wall. These pistonrings separate the spaces 6 and 21 from the compresllil ent in magnitudeand phase from that produced by the combination of piston and pistonrod. Summation of these two volume variations results in a givenvariation of the volume of the space 7, which involves a given pressurevariation of the medium in said space, which has an average pressurelevel below the average pressure levels in the spaces 6 and 21. 7

By an appropriate choice of the volumes of the spaces 6 and 21 and ofthe diameters of operation of the piston rings 8 and 23 it is ensuredthat with a given pressure level in said spaces during the movements ofthe piston and the displacer in the cylinder a pressure variation isobtained which always differs by a constant amount from the pressurevariation in the space 7. The pressure variations in the two spaces aretherefore equal to and in phase with each other. Medium diffused throughthe rolling diaphragm 5 and 20 is conducted back to the compressionspace 11 via the bypass valve 32 in the manner described with referenceto FIG. 1.

FIG. 3 shows a device corresponding largely with the device shown inFIG. 1. Corresponding parts are therefore designated by the samereference numerals. Apart sionspacell. The piston rings 8 and 23 areprovided on their lower sides with radial grooves. Consequently, thereis always an open communication between the spaces in the grooves behindthe piston rings and the spaces 6 and 21 so that in the operation of thedevice gas leakage willtake place mainly from the compression space 11into the spaces 6 and 21. As a result, an average pressure will beestablished in the spaces 6 and 21, which pressure will be higher thanthe average pressure in the compression space 1 1 and be approximatelyequal to the maximum pressure in the compression space. In operation thepiston 2 with the piston rod 4 and the displacer 10 move with a givenphase difference in the cylinder 1. Y

The extent of the volume variation of the space 7 is mainly determinedby the surface of the annular face 9 of the piston 2 and the length ofthe piston stroke. In addition small volume variations are produced bythe movements of the piston rod and the displacer rod, determined by thesurfaces of the lower sides of said rods and by the lengths of thestrokes of said rods. The volume variation produced by the displacer rodis differfrom the piston ring 8, separating the space 6 from the workingspace 3, this device comprises a piston ring 24 separating a space 25from the space 7. The piston rings 8 and 24 are both operative on adiameter equal to the effective diameter of the rolling diaphragm 5.Upon a movement of the piston 2 in the cylinder 1 the volume of thespaces 6 and 25 will remain constant so that no pressure variationsoccur in this space owing to volume variations, whereas the pressurevariations in the working space 3 and the space 7 respectively are nottransferred by the piston rings 8 and 24 respectively to the space 6 andthe space 25 respectively. Therefore, in each stroke a substantiallyconstant pressure difference will prevail across the rolling diaphragm.Medium diffused through the rolling diaphragm 5 into the space 7 isagain returned via the bypass valve 32 into the working space 3.

FIG. 4 shows an embodimentof a hot-gasengine of the displacer type,which corresponds mainly with the device shown in FIG. 2, so thatcorresponding reference numerals are used. Apart from the piston rings 8and 23 separating the spaces 6 and 21 from the compression space 11, apiston ring 26 is provided here between the piston wall and the cylinderwall, which ring separates a space 27 beneath the rolling diaphragm 5from the space 7, while a pistonring 28 is provided between the pistonwall and the displacer wall, which separates a space 29 beneath therolling diaphragm 20 from the space 7.

The piston rings 8 and 26 are both operative on the same diameter as theeffective diameter of the rolling diaphragm 5, whereas the piston rings23 and 28 are both operative on a diameter equal to the effectivediameter of the rolling diaphragm 20. This means that upon a relativemovement of the piston and the cylinder and the displacer respectively,the volumes of the spaces 6, 21, 7 and 29 remain constant, so that nopressure variations will occur in said spaces. The pressure variationsin the compression space 11 are not transferred by the piston rings 8and 23 respectively to the spaces 6 and 21 respectively whereas thepressure variations occurring in the space 7 cannot penetrate into thespaces 27 and 29 respectively because they are retained by the pistonrings 26 and 28 respectively.

The result is that on either side of the rolling diaphragm constant, butrelatively different pressures are always prevailing. The spaces 6 and21 communicate with each other by a channel 22 and the spaces 27 and 29are in open communication with each other via a channel 30. This has theadvantage that in case of any slight pressure variations in one of thespaces in the operation of the device, for example, due to tolerances ofthe relatively co-operating parts, these variations are levelled outsince said space communicates with a further space. Also this devicecomprises a return duct 31 with a bypass valve 32 so that mediumdiffused through the rolling diaphragms and into the space 7 is fed backinto the compression space 11.

Although in the drawing the rolling diaphragms are all shown in aposition in which the concave sides face the working space and thecompression space respectively, it is of course also possible, whilemaintaining the same advantages, to have the rolling diaphragms facetheir convex sides to the said spaces. As shown in the drawing the sealbetween the space adjacent the rolling diaphragm and the working spaceor compression space or the further space is formed by only one pistonring. It will be obvious that this seal may be formed by a plurality ofpiston rings.

It is furthermore shown that the piston ring has its side provided withradial grooves facing the rolling diaphragm so that in the spaceadjacent the rolling diaphragm a pressure will be established which isapproximately equal to the maximum pressure in the other space adjacentthe piston ring. As a matter of course the piston ring may be arrangedin the groove so that the side provided with the radial grooves isremote from the rolling diaphragm. The pressure then established in thespace between the rolling diaphragm and the piston ring is thenapproximately equal to the minimum pressure in the space adjacent theside of the piston ring provided with the radial grooves. The opencommunication between the space in the groove behind the piston ring andone of the two spaces separated by said piston ring may also be formedby the upper or lower surface of the groove in the piston-, cylinderordisplacer wall provided with radial slots or with bores.

Under given conditions the seal may also be'formed by a narrow gap, inwhich case the average pressure prevailing on the other side of the sealin the working space, the compression space or the further space will beproduced in the space between the rolling diaphragm and the seal.

From the foregoing it will be obvious that the invention provides anextremely simple construction of a device comprising rolling diaphragmsbetween piston, cylinder or rod, which diaphragms are on one side incontact with a gas-filled space, for example, a working space and on theother side with a gas supporting them, while a constant pressuredifference always prevails across these rolling diaphragms.

What is claimed is:

1. Compression apparatus comprising a cylinder, a piston axially movablein the cylinder, the piston having an outer body part with oppositecompression and remote end parts, the piston and cylinder having a firstset of adjacent walls corresponding to said body part remote end of thepiston and defining a first annular space between said walls, and asecond set of adjacent walls corresponding to said compression end partof the piston and defining a second annular space therebetween, thecompression end of the piston defining with the cylinder a variablevolume compression space for working medium containable therein, arolling diaphragm seal secured between said first set of walls anddefining and separating said first annular space into axially spacedfirst and second portions thereof for containing compressible medium atrelatively different average pressures, a second seal disposed in saidsecond annular space, axially between said first portion of the firstannular space and the compression space, the second seal having anoperative diameter unequal to the effective diameter of said firstrolling seal and operative as a one-way valve for providing a constantpressure differential across said first seal.

2. Apparatusaccording to claim 1 wherein said rolling seal has a concaveside facing said second seal, and said second seal permits gas flow onlytoward the rolling seal from the compression space.

3. Apparatus according to claim 1, wherein at least one of the walls ofsaid first set has a stepped diameter such that the volume of said firstouter annular space remains constant during axial movement of thepiston.

4. Apparatus according to claim 1 wherein said second portion of thefirst outer annular space is in open communication with the remotespace, the second seal (having an operative diameter different from theeffective diameter of the rolling diaphragm) produces volume variationsof the first portion of the first outer annular space and resultantpressure variations in said first portion space which are at leastsubstantially equal to and in phase with the pressure variationsoccurring in the remote space and in the second portion of the firstouter annular space communicating therewith, the average pressure insaid first portion differing from that in the remote space and in thesecond portion.

5. Apparatus according to claim 1 wherein said pistons remote end andthe cylinder define a third set of adjacent walls defining a thirdannular space, the apparatus further comprising a third seal disposed insaid third annular space, this third seal being operative on the samediameter as the effective diameter of the rolling diaphragm.

6. Apparatus according to claim 1 wherein said second seals comprisepiston rings, and said apparatus includes for each ring a groove in oneof the adjacent walls of said piston and cylinder, anddisplacerconnecting rod and piston, and communication means is providedbetween said groove and one of said two spaces on the opposite sides ofsaid seal.

7. Apparatus according to claim 1 wherein said second seals are formedby narrow gaps.

8. Apparatus according to claim 1 further comprising duct meanscommunicating said working space with said remote space, a by-pass valvewithin said duct means opening toward said working space which isfacingthe concave side of said rolling diaphragm seal.

9. Apparatus comprising a cylinder, a piston axially movable in thecylinder, the piston having a body part and a compression end part, thelatter part cooperating with the cylinder to define a variable volumeworking space containing a working medium, the cylinder and pistonhaving first and second pairs of adjacent wall surfaces correspondingrespectively to said body and end parts of the piston, a first rollingdiaphragm seal secured between said first adjacent surfaces andseparating a first annular space from a second annular space,

these spaces containing working medium of different second adjacentsurfaces and separating said first annular space from said workingspace, at least one of said piston and cylinder wall surfaces extendingbetween said first rolling seal and said first ring seal defining astepped construction, and said first ring seal having an effectivediameter substantially equal to that of the first rolling seal, suchthat the pressure differential between the first and second annularspaces across said first rolling seal is substantially constant.

10. Apparatus according to claim 9 wherein the piston has the remote endopposite the compression end and the piston remote end and thecorresponding cylinder part have third adjacent wall surfaces, theapparatus further comprising a second ring seal secured between saidthird adjacent surfaces with the second annular space between said firstrolling seal and said sec-. ond ring seal, this second ring seal havingAn effective diameter equal to that of the first ring seal.

11. In a hot-gas engine including a cylinder, a compression pistonreciprocally movable in the cylinder, a displacer to which is connecteda displacer rod that extends through the bore in said piston with avariable volume compression space defined between said piston anddisplacer, said piston having a body part and a compression end part,the cylinder and piston having first and second adjacent wall surfacescorresponding respectively to the body and compression end parts of saidpiston, a first rolling diaphragm secured between said first adjacentsurfaces and separating a first annular space from a second annularspace, these spaces containing working medium at different averagepressures, a first ring seal secured between said second adjacentsurfaces and separating said first annular space from said compressionspace, at least one of said piston and cylinder wall surfaces extendingbetween said first rolling seal and said first ring seal defining astepped construction, said first ring seal having an effective diametersubstantially equal to that of the rolling seal, such that the pressuredifferential between said first and second annular spaces across saidrolling seal is substantially constant, said apparatus furthercomprising third and fourth adjacent wall surfaces between said rod andpiston bore and similar to said first and second adjacent wall surfacesand rolling and ring seals therebetween.

12. An engine according to claim 11 wherein said piston has a remote endopposite the compression end, and the piston remote end andcorresponding cylinder part have fifth adjacent wall surfaces, and saidpiston remote end and displacer rod therethrough also have sixthadjacent wall surfaces, the apparatus further comprising third andfourth ring seals secured respectively between the fifth and sixthadjacent wall surfaces, said third and fourth ring seals each having aneffective diameter equal to that of the first and second ring sealsrespectively, such that the pressure differential across the rollingdiaphragm seals is substantially constant.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,783,715 Dated ry 197# Inventor(s) Roelf Jan Meijer et a1.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

In the Title Page: After "Related U. S. Application Data Continuation ofSer. No. 26,580, April 8, 1970 abandoned." insert Foreign ApplicationPriority Data April 1'7, 1969 Netherlands ...,.6905902 Col. 5, line 1,before "space" insert remote line 9, before "space" (second occurrence)insert remote Col. line 61, before 'space" second occurrence insertremote Signed and sealed this 3rd day of September 197A.

(SEAL) Attest: I

MCCOY M. GIBSON, JR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents FORM POJOSP (10.69) USCOMM-DC 60376 P69 fl' U.S.GOVERNMENTPRINTING OFFICE: IBIB D366-334,

1. Compression apparatus comprising a cylinder, a piston axially movablein the cylinder, the piston having an outer body part with oppositecompression and remote end parts, the piston and cylinder having a firstset of adjacent walls corresponding to said body part remote end of thepiston and defining a first annular space between said walls, and asecond set of adjacent walls corresponding to said compression end partof the piston and defining a second annular space therebetween, thecompression end of the piston defining with the cylinder a variablevolume compression space for working medium containable therein, arolling diaphragm seal secured between said first set of walls anddefining and separating said first annular space into axially spacedfirst and second portions thereof for containing compressible medium atrelatively different average pressures, a second seal disposed in saidsecond annular space, axially between said first portion of the firstannular space and the compression space, the second seal having anoperative diameter unequal to the effective diameter of said firstrolling seal and operative as a one-way valve for providing a constantpressure differential across said first seal.
 2. Apparatus according toclaim 1 wherein said rolling seal has a concave side facing said secondseal, and said second seal permits gas flow only toward the rolling sealfrom the compression space.
 3. Apparatus according to claim 1, whereinat least one of the walls of said First set has a stepped diameter suchthat the volume of said first outer annular space remains constantduring axial movement of the piston.
 4. Apparatus according to claim 1wherein said second portion of the first outer annular space is in opencommunication with the remote space, the second seal (having anoperative diameter different from the effective diameter of the rollingdiaphragm) produces volume variations of the first portion of the firstouter annular space and resultant pressure variations in said firstportion space which are at least substantially equal to and in phasewith the pressure variations occurring in the remote space and in thesecond portion of the first outer annular space communicating therewith,the average pressure in said first portion differing from that in theremote space and in the second portion.
 5. Apparatus according to claim1 wherein said piston''s remote end and the cylinder define a third setof adjacent walls defining a third annular space, the apparatus furthercomprising a third seal disposed in said third annular space, this thirdseal being operative on the same diameter as the effective diameter ofthe rolling diaphragm.
 6. Apparatus according to claim 1 wherein saidsecond seals comprise piston rings, and said apparatus includes for eachring a groove in one of the adjacent walls of said piston and cylinder,and displacer-connecting rod and piston, and communication means isprovided between said groove and one of said two spaces on the oppositesides of said seal.
 7. Apparatus according to claim 1 wherein saidsecond seals are formed by narrow gaps.
 8. Apparatus according to claim1 further comprising duct means communicating said working space withsaid remote space, a by-pass valve within said duct means opening towardsaid working space which is facing the concave side of said rollingdiaphragm seal.
 9. Apparatus comprising a cylinder, a piston axiallymovable in the cylinder, the piston having a body part and a compressionend part, the latter part cooperating with the cylinder to define avariable volume working space containing a working medium, the cylinderand piston having first and second pairs of adjacent wall surfacescorresponding respectively to said body and end parts of the piston, afirst rolling diaphragm seal secured between said first adjacentsurfaces and separating a first annular space from a second annularspace, these spaces containing working medium of different averagepressures, a first ring seal secured between said second adjacentsurfaces and separating said first annular space from said workingspace, at least one of said piston and cylinder wall surfaces extendingbetween said first rolling seal and said first ring seal defining astepped construction, and said first ring seal having an effectivediameter substantially equal to that of the first rolling seal, suchthat the pressure differential between the first and second annularspaces across said first rolling seal is substantially constant. 10.Apparatus according to claim 9 wherein the piston has the remote endopposite the compression end and the piston remote end and thecorresponding cylinder part have third adjacent wall surfaces, theapparatus further comprising a second ring seal secured between saidthird adjacent surfaces with the second annular space between said firstrolling seal and said second ring seal, this second ring seal having Aneffective diameter equal to that of the first ring seal.
 11. In ahot-gas engine including a cylinder, a compression piston reciprocallymovable in the cylinder, a displacer to which is connected a displacerrod that extends through the bore in said piston with a variable volumecompression space defined between said piston and displacer, said pistonhaving a body part and a compression end part, the cylinder and pistonhaving first and second adjacent wall surfaces correspondingrespectively to the body and compression end parts of said piston, afirst rolliNg diaphragm secured between said first adjacent surfaces andseparating a first annular space from a second annular space, thesespaces containing working medium at different average pressures, a firstring seal secured between said second adjacent surfaces and separatingsaid first annular space from said compression space, at least one ofsaid piston and cylinder wall surfaces extending between said firstrolling seal and said first ring seal defining a stepped construction,said first ring seal having an effective diameter substantially equal tothat of the rolling seal, such that the pressure differential betweensaid first and second annular spaces across said rolling seal issubstantially constant, said apparatus further comprising third andfourth adjacent wall surfaces between said rod and piston bore andsimilar to said first and second adjacent wall surfaces and rolling andring seals therebetween.
 12. An engine according to claim 11 whereinsaid piston has a remote end opposite the compression end, and thepiston remote end and corresponding cylinder part have fifth adjacentwall surfaces, and said piston remote end and displacer rod therethroughalso have sixth adjacent wall surfaces, the apparatus further comprisingthird and fourth ring seals secured respectively between the fifth andsixth adjacent wall surfaces, said third and fourth ring seals eachhaving an effective diameter equal to that of the first and second ringseals respectively, such that the pressure differential across therolling diaphragm seals is substantially constant.